This invention relates to the inhibition of corrosion of metal surfaces and more particularly to the inhibition of corrosion of copper or copper alloy surfaces in heat transfer equipment.
Metal surfaces which are in continuous contact with water or aqueous liquids, particularly aqueous liquids that contain chemicals or mineral salts, generally undergo considerable corrosion. To extend the life of the metal surfaces it is common practice to add small amounts of certain chemical substances to the aqueous liquid to inhibit corrosion of the metal surfaces.
Copper metal and copper alloys, which are often used in heat transfer equipment because of their superior heat transfer properties, are particularly susceptible to corrosion. One class of organic compounds, the aromatic triazoles, have been found to be quite effective in inhibiting the corrosion of copper metal. The triazole molecule appears to form a complex with the copper on the surfaces of the metal thereby forming a coating on the metal surfaces which protects the surfaces from the effects of corrosive materials. Several patents and literature references describe the use of aromatic triazoles alone or in combination with other chemical compounds as corrosion inhibitors. U.S. Pat. No. 3,265,620, issued to Heiman, discloses metal working coolants containing diethanolamine, benzotriazole and the tetrasodium salt of ethylene diaminetetraacetic acid. U.S. Pat. No. 3,291,741, issued to Maciejewski et al, discloses an anticorrosive composition comprised of, inter alia, benzotriazole and 4,4-bis(3-nitro-4 hydroxyphenyl)pentanoic acid. U.S. Pat. No. 4,197,210, issued to Bridger, discloses a lubricant composition comprised of an oil-soluble adduct of benzotriazole and a dialkylamine. U.S. Pat. No. 3,553,137, issued to Woods, discloses a three component corrosion inhibitor for methoxypropanol comprised of an alkali metal nitrite, a piperazine and benzotriazole. Polish Pat. Nos. 90115 (see Chemical Abstract 90:74229m) and 95752 (see Chemical Abstract 91:23747s) disclose mining apparatus hydraulic fluids containing benzotriazole and an emulsifying oil containing diethanolamine. Razrab. Mer Zashch. Met. Korroz., Mezhdunar. Nauchno-Tekk. Konf. Probl. SEV. 3rd, 1980, 3, 47-50 (see Chemical Abstract 95:136895q) discloses a volatile corrosion inhibitor comprised of hydroxybenzotriazole and diethanolamine. Japanese Pat. No. 57049677 and Japanese Pat. No. 8249677 disclose methylbenzotriazole amine and diethanolamine benzotriazole salts as corrosion inhibitors for aqueous inks. Japanese Pat. No. 8223071 discloses a cooling system corrosion inhibitor comprised of benzotriazole and diethanolamine. Japanese patent application 8017864 discloses a corrosion inhibitor for wire enamels comprised of the diethanolamine salt of benzotriazole. British Pat. No. 2,080,342 discloses a composition for improving rust resistance comprised of an aliphatic dicarboxylic acid and 1-hydroxybenzotriazole.
Quite often there is a tendency for bacteria to accumulate and multiply in cooling water systems. To counteract the growth of bacteria, water soluble hypochlorites, such as sodium hypochlorite and other chlorine-containing compounds which form hypochlorite ions, are added to the cooling water. Although these compounds are effective biocides, they interfere with the aromatic triazole, apparently by combining with the triazole. Another problem encountered in the use of aromatic triazoles in cooling water systems is that the cooling water often contains small amounts of copper ions. These copper ions also combine with the aromatic triazoles thereby reducing the amount of aromatic triazole that is available for the protection of the metal surface.
Because of the effectiveness of aromatic triazoles in inhibiting corrosion of metal surfaces it would be desirable to eliminate the interference of chlorine-containing compounds with the corrosion inhibiting effectiveness of aromatic triazoles. It would be very beneficial if the interference of both chlorine-containing compounds and copper ions with the effectiveness of the triazoles could be eliminated at the same time.